tests: clitest: Cover all --memorybacking options and aliases

tests/cli-test-xml/compare/virt-install-singleton-config-3.xml

@@ -8,6 +8,11 @@
   </metadata>
   <memory>1048576</memory>
   <currentMemory>1048576</currentMemory>
+  <memoryBacking>
+    <hugepages/>
+    <access mode="shared"/>
+    <source type="anonymous"/>
+  </memoryBacking>
   <vcpu>6</vcpu>
   <os>
     <type arch="x86_64" machine="q35">hvm</type>

tests/clitest.py

@@ -486,6 +486,7 @@ c.add_compare("""
 --memory 1024
 --disk none
 --boot bios.useserial=no,bios.rebootTimeout=60,cmdline=root=/foo,smbios.mode=host,bootmenu.enable=yes,loader_ro=yes,loader.type=rom,loader=/tmp/foo
+--memorybacking access.mode=shared,source.type=anonymous,hugepages=on
 --graphics spice,gl=yes
 --rng egd,backend.type=nmdm,backend.source.master=/dev/foo1,backend.source.slave=/dev/foo2
 --panic default,,address.type=isa,address.iobase=0x500,address.irq=5